1. Field of the Invention
The present invention relates generally to an apparatus for centering a vehicle steering wheel with respect to a vertical axis of the steering wheel More particularly, the present invention relates to an apparatus and method for centering the vehicle steering wheel as the steering wheel rotates freely with respect to the vehicle body.
2. Disclosure Information
When the roadwheels of a vehicle are in a straight ahead position, the vehicle steering wheel should be in a central neutral position allowing the vehicle operator a clear view of the instrument panel. This position, also known as the clear vision position, refers to a position of a spoke of the steering wheel to an imaginary vertical axis of the steering wheel. Typically, because of compliance in the vehicle steering system due to the connections of the steering shaft to the steering gear, the steering gear to the tie rods and the tie rods to the vehicle wheels, vehicle manufacturers specify a preselected tolerance about the vertical axis that the steering wheel can move and still be within a clear vision position. This tolerance and the position of the steering wheel with respect to its vertical axis define a relationship with the position of the vehicle roadwheels. Specifically, this relationship corresponds to a predetermined toe angle of the vehicle roadwheels. Typically, in a steering wheel having a single spoke extending laterally across the diameter of the steering wheel, the clear vision position is that position wherein the spoke lies generally Perpendicular to the vertical axis of the steering wheel and the roadwheels are in the straight ahead position.
As stated above, it is desirable to position the steering wheel in its clear vision position when the wheels are in the straight ahead position so that the vehicle operator's view of the instrument panel is unobstructed when the vehicle is traveling straight. Furthermore, if the steering wheel is not in its clear vision position, later operation of the vehicle with the steering wheel in a centered position will cause the vehicle to turn because the wheels are not in the straight ahead position.
Various devices have been proposed for positioning the steering wheel in a clear vision position during alignment of the vehicle roadwheels. For example, U.S. Pat. No. 4,893,413 and the devices described therein, as well as U.S. Pat. Nos. 4,679,327 and 2,598,599 disclose steering wheel centering apparatuses wherein the steering wheel is locked into the clear vision position before alignment of the vehicles is begun. The '327 patent discloses the use of an inclinometer to set the steering wheel to a desired position before alignment of the vehicle wheels is begun. These devices suffer from the disadvantage that during the straightening of the roadwheels with the steering wheel locked in position, compliance in the steering system increases, resulting in a potentially large degree of offset of the steering wheel from the centered position after the steering wheel is unlocked and the vehicle begins to move. Therefore, there is a need to reduce the compliance buildup of the steering system while the steering wheel is positioned to achieve clear vision.
U S. Pat. No. 4,393,694 discloses a system wherein a torque wrench is attached to the steering wheel and torque is measured in each steering direction. From these two steps, front end alignment defects can be determined. However, the steering wheel cannot be set to a clear vision position accurately with this system.
U.S. Pat. No. 3,889,527 discloses a system which measures the angular rotation of the steering wheel to determine the amount of compliance in the suspension system. The system is not used to set the steering wheel to a clear vision position.
It is a feature of the present invention to provide an apparatus which positions the vehicle steering wheel to correspond to the position of the vehicle roadwheels.
It is a further feature of the present invention to provide an apparatus which aligns the vehicle roadwheels to a predetermined toe angle corresponding to the instantaneous position of an unfixtured steering wheel so that the steering wheel is in a clear vision position when the roadwheels are in a straight ahead position.
It is an advantage of the present invention to provide an apparatus which eliminates steering system compliance buildup during the alignment process.
It is a further advantage of the present invention that the steering wheel may be set to a clear vision position more accurately than with prior art systems.
These and other objects, features and advantages of the present invention will become apparent from the summary, detailed description and claims which follow.